Rainbow Electronics CAN интерфейс - Manual (Page 53)

BOSCH
ROBERT BOSCH GmbH, Postfach 300240, D-7000 Stuttgart 30
Sep. 1991
Part B - page 51
FLAG. So the sequence of ’dominant’ bits which actually can be monitored on the bus
results from a superposition of different ERROR FLAGs transmitted by individual
stations. The total length of this sequence varies between a minimum of six and a
maximum of twelve bits.
An ’error passive’ station detecting an error condition tries to signal this by transmission
of a PASSIVE ERROR FLAG. The ’error passive’ station waits for six consecutive bits
of equal polarity, beginning at the start of the PASSIVE ERROR FLAG. The PASSIVE
ERROR FLAG is complete when these 6 equal bits have been detected.
ERROR DELIMITER
The ERROR DELIMITER consists of eight ’recessive’ bits.
After transmission of an ERROR FLAG each station sends ’recessive’ bits and
monitors the bus until it detects a ’recessive’ bit. Afterwards it starts transmitting seven
more ’recessive’ bits.
3.2.4 OVERLOAD FRAME
The OVERLOAD FRAME contains the two bit fields OVERLOAD FLAG and
OVERLOAD DELIMITER.
There are two kinds of OVERLOAD conditions, which both lead to the transmission of
an OVERLOAD FLAG:
1. The internal conditions of a receiver, which requires a delay of the next DATA
FRAME or REMOTE FRAME.
2. Detection of a ’dominant’ bit at the first and second bit of INTERMISSION.
3. If a CAN node samples a dominant bit at the eighth bit (the last bit) of an ERROR
DELIMITER or OVERLOAD DELIMITER, it will start transmitting an OVERLOAD
FRAME (not an ERROR FRAME). The Error Counters will not be incremented.
The start of an OVERLOAD FRAME due to OVERLOAD condition 1 is only allowed to
be started at the first bit time of an expected INTERMISSION, whereas OVERLOAD
FRAMEs due to OVERLOAD condition 2 and condition 3 start one bit after detecting
the ’dominant’ bit.
Overload Frame